In a small pot, combine water, brown sugar, and a cinnamon stick. Heat until it simmers for 2-3 minutes, stirring until dissolved. Remove from heat, add vanilla extract, and steep chai tea bags for 10 minutes. Cool and store syrup in the fridge.

Fill a shaker glass with ice cubes, pour in espresso, add syrup and ground cinnamon. Shake vigorously for about 1 minute until cold.

In a tall glass filled with ice, strain the espresso mixture. Pour oat milk over the top until desired creaminess is achieved.

Garnish with ground cinnamon or a sprig of lavender. Serve immediately.